Superregenerative receiving system



Feb M, i936.

N. M. RUST ET AL SUPERREGENERATIVE RECEIVING SYSTEM Filed April 19, 1955 2 Sheets-Sheet l Alik- ATTORNY Feb. l, 1935. N- M RUST ET AL 2,939,120 I SUPERREGENERATIVE RECEIVING SYSTEM Filed April 19, 1933 2 Sheets-Sheet 2 lill- ATTORNEY Patented Feb. 11, 1936 UNITEDl STATES SUPERREGENERATIVE RECEIVING SYSTEM Nol Meyer Rust and Robert Francis ONeill,

Chelmsford, England, assignors to Radio Corporation of America, a corporation of Delaware Application April 19, 1933, Serial No. 666,866 In Great Britain April 22, 1932,

10 Claims. (Cl. Z50-20) This invention rel-ates to radio and other high frequency receivers and more particularly to receivers of the soi-called super-regenerative type i. e. receivers wherein an oscillating detector cir-` ;f cuit arrangement is periodically damped so that the oscillations thereof are periodically quenched e. g. at supersonic frequency.

The present invention makes use of the fact that certain forms of electronic valves under me suitable conditions of operating potentials will inherently exhibit negative resistance effects. Such valves are herein referred to as negative resistance Valves. For example, the anode currentanode voltage characteristic of the well-known screened grid valve is a curve having a sharply rising portion followed by a. portion which is substantially linear and which slopes downwardly, this falling portion being again followed by a rising portion. It will be apparent that between y the two rising portions of the characteristic i. e. over the falling portion, the valve inherently exhibits negative resistance effects (that is, the negative resistance is obtained without any external feed-back circuit) and, as is known if one or more resonant circuits of suitable constants be included in the circuit of a screened grid valve, and if the potentials applied to the electrodes of that valve are chosen within certain limits, the valve will generate oscillations at the frequency 3 or frequencies vof the tuned circuit or circuits. Indeed this property of the screened grid valve has already been put into practical use to provide an oscillation generator, which oscillates by virtue of the negative resistance characteristics of 3:4 the Valve.

According to this invention, a negative resistance valve is utilized to provide the necessary oscillatory periods in a radio or other high frequency receiver operating on the so-called superregenerative principle means being, of course,

provided for quenching the oscillations periodically and as required by the said super-regenerative principle.

It will be appreciated that if a screened grid 4,3 valve or other electronic valve having a characteristic of similar form (i. e. other negative resistance valve) be so adjusted as to operate round one of the bends at the ends of the downwardly sloping portion of the characteristic and if a 50 tuned circuit or circuits of suitable constants be connected in the output circuit of said valve, the whole circuit arrangement will change from a condition of overall negative resistance i. e. from a condition in which oscillations would ultimate- 55 ly build up to a condition in which they would not, and vice versa as the valve in operating moves back 4and. forth round the bend in its characteristic. This phenomenon is utilized in one way of carrying the present invention into prac- 60 tice and, in one form of construction, therefore,

a super-regenerative radio or like high frequency circuit may comprise a detector valve; a high frequency resonant circuit associated therewith; a negative resistance electronic valve (e. g. a screened grid valve) associated with the said 5 resonant circuit; a periodic circuit also associated with said negative resistance valve and operating at a frequency lower than that of said tuned circuit; and means for applying operating potentials to the electrodes of said negative resistance valve, so that the negative resistance valve operates around one of the bends at the ends of the negative resistance portion of its characteristic whereby oscillations are periodically set up and quenched in the tuned circuit of the detector valve, the periodicity of setting up and quenching being determined by the frequency of operation of the periodic circuit which may, for example, be constituted by a tuned circuit having a supersonic natural frequency.

There are, however, other Ways of carrying the invention into practice. For example, in one modified arrangement in accordance with the invention, two separate valves are employed in addition to the detector valve, one being a screened grid valve or other negative resistance electronic device for providing the necessary regeneration and the other providing the periodic damping. During the major portion of a cycle of operations of the superregenerative receiver the tetrode is in the negative resistance state and during the relatively short period per cycle during which quenching is required the valve providing the damping is rendered conductive the negative resistance valve being inoperative during this short period per cycle. The change between the different conditions holding during the two portions of the cycle of operations is brought about quite sharply and suddenly by applying a pulse of E. M. F. simultaneously to an electrode of the tetrode and to an electrode of the damping valve. These pulses are applied by a periodic circuit which may, for example, be constituted by a leaky condenser and electric discharge lamp combination which controls in a periodic manner the operating bias potentials applied to the two auxiliary valves, namely, the negative resistance valve and the damping valve.

In a further modification of the last described arrangement a separate damping or quenching valve is dispensed w'ith and the periodic circuit is caused to produce the required result by acting upon the negative resistance valve alone,

Various forms of construction in accordance with the invention will now be described in detail and illustrated in the accompanying drawings.

In one form of construction illustrated in the accompanying drawings a detector constituted by a triode I having the usual grid condenser 2,

grid leak 3 and grid bias battery 4 (grid leak or 60- anode bend detection may be employed as desired) associated with its grid contains in its grid circuit a radio frequency tuned circuit 5, 6, (to which s ignals are applied) said tuned circuit being in series with a second tuned circuit 5A, 6A, operating at a supersonic frequency or at a high audio frequency as may be convenient. The grid circuit of the detector Valve thus extends from the grid, through the grid condenser 2, through the radio frequency tuned circuit, 5, 6, through the second tuned circuit 5A, 6A, through part of a potentiometer resistance 24 ,across a battery 25 back to the cathode. The tuned circuits 5, 6 and 5A, 6A, are also included in the plate circuit of a screen grid valve 28, said plate circuit extending from the plate through the tuned circuits 5, 6, and 5A, 6A and thence through a portion of the potentiometer resistance 24 to the cathode of the screened grid valve, this cathode being joined to the cathode of the triode by a lead 21. The battery 25 thus provides anode potential for the screen grid valve and also potential to the screening grid thereof, the latter potential being larger than that applied to the anode. The tuned circuit 5A, 6A, includes a preferably adjustable series resistance 28 which is so chosen or so adjusted that the relative damping of the two tuned circuits 5, 6 and 5A, 6A is such that the screened grid valve will oscillate at the frequency of the circuit 5A, 6A and shift the working point of the valve round one of the bends at the ends of the negative resistance portion of its characteristic. The adjustable resistance 28 though not essential is of considerable practical advantage since it provides a means of controlling the degree of quenching. Operation may be obtained around either bend and the bend utilized Will depend upon the adjustment of the ,anode potential of the screened grid valve. In this way the tuned circuit 5, S, is caused, in effect, alternately to have negative and positive resistance characteristics at the frequency of the circuit 5A, 6A. The dynamic conductance of the radio frequency circuit should ,always be higher than that of the supersonic circuit, while the average conductance over a supersonic frequency cycle of operations should be negative and equal to the dynamic conductance of the supersonic frequency circuit but less than that of the radio frequency circuit.

Owing to the fact that the sum of the anode current and of the screen grid current remains approximately constant as the anode voltage is varied and that therefore variations of anode current are accompanied by equal ,and opposite variations of screen grid current, it is possible to dispense with the use of a separate detector valve and, for example, to connect the telephones or other output device in the circuit of the screen grid, e. g. the output device may be inserted between the points at, :l: shown on the screen grid lead in the accompanying drawings.

Alternatively, the output device may be directly connected in the anode circuit of the screen grid valve, but with the particular arrangement shown in the accompanying drawings the connection of the output device in the the screened grid circuit is preferred since if the output device be inserted in the anode circuit, special precautions must be taken to bypass thesaid output device.

As will be appreciated similar considerations apply to circuit arrangements as described below, and-in these said arrangements also the use of a of the valve I by means of the usual tuned circuit consisting of an inductance 5 and shunt tuning condenser 6 said circuit being coupled at one end through the condenser 2 to the grid of the valve I.

The anode circuit of the valve I includes the usual output device which is connected at the terminals 1, anode potential being applied to the valve I from a battery 8. Regeneration is obtained by means of a negative resistance screened grid valve 9 whose plate is connected to the grid end of the tuned input circuit 5, 6, and whose cathode is connected to a movable tapping point I0 upon a potentiometer resistance II. Control grid bias for the valve 9 is obtained by means of an adjustable potentiometer I2 in association with a battery I3 as shown, the total bias upon this control grid including also any potential which may occur across that part of the resistance II which is included between grid and cathode of the said valve 9. Screen grid potential is applied to the Valve 9 from the battery 8 as shown. Damping is obtained by means of a further auxiliary valve, in this case constituted by a triode I4, whose plate is connected to the plate of the valve 9 and whose cathode is connected to the cathode thereof Bias is applied to the control grid of the valve I4 by means of a battery I5, the total bias applied including, in addition to the potential of this battery I5, any potential which may occur across that part of the resistance II which is included in the circuit between the control gridof said valve I4 and the cathode thereof. The operating conditions of the whole circuit are changed periodically by means of a periodic circuit which consists of the battery 8, a neon or other glow discharge tube I6, a condenser I1 (preferably variable for adjustment purposes) a resistance I8 (also preferably adjustable) and the resistance II all in series.

As is well known the neon lamp in a circuit such as this will wink periodically due to the charging and discharging of the condenser I1 the periodicity of winking being, of course, controlled by the capacity and resistance in circuit. It will be appreciated that the condenser I1 will charge and discharge itself automatically and in a periodic manner (the neon tube I6 flashing during each charging action i. e. each time the condenser I1 loses its charge) to such an extent that the potential across the terminals of the tube I6 is greater than the ignition voltage thereof. Each time the neon tube flashes a current iiow will occur through the resistance I I in the direct current circuit 8, I6, I1, I8, I I and a pulse of electromotive force Will be applied to the control grids of the valves 9 and I4 relative to their cathodes. The circuitV adjustments are such that except when these pulses occur the valve 9 exhibits negative resistance (the said valve should be adjusted so as normally to give maximum negative resistance) while the valve I4 is non-conductive. These conditions apply during the major portion of each cycle of operation. The occurrence of a pulse, however, renders the valve I4 conductive and reduces the negative conductance of the .lill

valve 9 to a small value so that for a relatively short period per cycle quenching is effected as is required by the super-regenerative principle. Adjustment of the action of the Valves 9 and I4 can be obtained by moving the movable point l upon the resistance Il.

It should be noted firstly that the anode potential of the valves 9 and I4 is not changed in the cycle of operations, any changes which may occur being at the radio frequency and incidental to the signals being received. If the constants of the glow discharge or blink circuit are correctly chosen, and in fact with the constants normal to the proper operation of the blink circuit, the flash time (during which the tube conducts and the condenser I1 receives its charge) is very short indeed, and even at high frequencies the period of extinction (during which the condenser II discharges through resistance I8) is relatively much longer. It should further be noted that as the circuit is arranged, no current ows through resistance Il whilst the condenser I1 is discharging, the only current flow taking place when the tube It flashes. Both the above features result in improved super-regeneration.

The first allows a lower note to be used without causing interference, and the second allows the largest possible build-up time for super-regeneration and thus for a given note obtains the optimum super-regenerative effect.

Another fact that can be utilized to advantage is that when the change from super-regeneration to quenching occurs the rise in anode current of the quenching valve can be made just equal to the drop of anode current of the negative resistance valve; this also results in a minimum amount of interference from the control note.

Figure 3 of the drawings illustrates a modification of the arrangement shown in Figure 2, the principal differences between the arrangements of Figures l and 2 of the specification being that in the latter arrangement a separate damping valve is dispensed with, the blink or periodic circuit operating direct upon the tetrode 9. In the said Figure 3 the resistance I9 is of such value that when the glow lamp flashes the voltage upon the outer or screening grid is reduced to a value sufficient to obtain the desired quenching action. It will be noted that control of the inner or control grid potential is also obtained in the said Figure 3 by reason of the fact that said grid is connected to a tapping upon a resistance 23 also in the blink circuit. This, however, is not necessary and outer grid control only, may, if desired, be utilized, the control grid being maintained at a xed potential.

A further directly acting arrangement (i. e. an arrangement in which the periodic circuit acts directly and solely upon the negative resistance valve) is shown in Figure 4 of the drawings the control in this case being obtained by utilizing the blink circuit to change the anode potential of the valve 9 by reason of voltage drop which occurs in the resistance 20 when the glow lamp flashes. Numeral ZI is a by-pass condenser which should be as small as possible and may-if other conditions of working permitbe omitted altogether in said Figure 4 the direct current circuit through the glow discharge tube I6 is as follows: Glow tube I6, circuit I'I, I8, resistor 20 and battery 8 back to the tube. It is obvious that the drop across the resistor 29 affects the potential on the anode of the tube 9 so that periodical discharges of the condenser I1 periodically affect the Work of tube 9.

Yet another directly acting arrangement is shown in Figure of the drawings wherein the blink circuit is utilized to control the cathode potential of the valve 9. Here the valve .9 is shown as of the indirectly heated cathode type and, as will be seen, the cathode proper is connected to a tapping point upon a resistance 22 in the blink circuit. Thus when a discharge occurs in the glow lamp the cathode receives a pulse of positive potential. This, of course, is

electrically equivalent to applying a pulse oi',

negative potential to the control grid. When the glow lamp discharges it also acts as a damping resistance thus quenching the incipient oscillations. In said Figure 5 the glow tube discharge current passes through a resistor 22 which affects the cathode of tube 9 thereby affecting the working characteristics of tube 9 periodically.

It will be apparent to those skilled in the/art that other methods of utilizing the periodic circuit to produce the desired result are possiblefor example, two or more of the various expedients embodied in the arrangements shown in Figures 2, 3 and 4 of the specification for directly controlling the negative resistance valve by a blink circuit, may be employed in combination. Again periodic circuit arrangements other than those herein specifically described may be employed-for example, oscillator control in place of discharge lamp blink circuit control may obviously be employed,

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed we declare that what we claim iszl. A radio receiver comprising in combination, an electron dis-charge detector tube having an input and an output circuit, the input circuit including a resonant circuit tuned to the frequency of signal energy desired to be received, a second electron discharge tube provided with external circuits connected so as to produce a. negative resistance effect across two points of said external circuits, circuit elements common to one of said detector tube circuits and one of the second electron discharge tube external circuits and connected between said two points whereby negative resistance effects are transferred to the detector tube and means connected with said external circuits for periodically rendering the second discharge tube inoperative to produce any negative resistance eiects across said terminals.

2. In a radio receiver of the super-regenerative type, an electron discharge detector having an input circuit and an output circuit, the input circuit including a resonant circuit tuned to the frequency of signal energy desired to be received, a second electron discharge tube comprising an electron emitting cathode, an anode and at least one grid electrode, external circuits including sources of potential connected to said second vtube elements and adapted to apply potentials to the tube elements of such relative values that the said second tube produces a negative resistance effect between the cathode and one of the other tube elements, means, forming part of said external circuits, for periodically varying the value of the negative resistance effect between said two electrodes, and means for connecting said resonant circuit between said two electrodes whereby the periodically varying negative resistance effects are transferred to the detector tube.

3. In a super-regenerative receiver, a detector tube provided with input and output circuits, the input circuit including a resonant circuit adapted to be tuned over a range of frequencies, a resistance circuit comprising an electron discharge device pro-vided with an anode, a cathode and at least one control electrode, external circuits connected with said electrodes and including sources of potential whereby the control electrode is normally maintained at a higher positive potential with respect to the cathode than the anode whereby said device normally exhibits a negative resistance characteristic between the cathode and the anode thereof, sai-d external circuits being arranged with respect to said resonant circuit so that said resonant circuit is included in a connection between the anode and cathode of said electron discharge device 'thereby normally provi-ding a negative resistance in shunt with the resonant circuit, said normally negative resistance across said resonant circuit acting to permit the detector tube to operate above its point of oscillation, and meann forming part of the external circuits associated with the electron discharge device for periodically affecting said electron discharge device to the extent that the negative resistance characteristic exhibit/ed between the anode and cathode thereof is changed to a positive resistance characteristic whereby there is, in effect, connected periodically across sai-d resonant circuit a positive resistance acting to permit the detector tube to -operate below its point of oscillation.

4. In a super-regenerative receiver, a detector tube provided with an input circuit and an output circuit, said input circuit including a signal input circuit adapted to be tuned over a range of frequencies, means for operating said detector tube above and below the point of oscillation to produce super-regenerative acti-on comprising, an electronic tube connected as a dynatron oscillator said electronic tube being connected in sai-d input circuit, means for causing said dynatron oscillator tube to alternately and periodically impress upon said input circuit negative and positive resistance characteristics.

5. In a super-regenerative receiver an electron discharge detector tube provided with an input circuit and an output circuit, said input circuit including a signal input circuit adapted to be tuned over a range of frequencies, means for operating said detector tube above and below the point of oscillation thereof to produce super-regenerative action said means comprising a dynatron circuit and means including a glow discharge tube operating in conjunction with a condenser charging circuit for causing said dynatron circuit to alternately and periodically impress upon the input circuit of the detector tube negative and positive resistance characteristics.

6. A system as described in the next preceding claim wherein said dynatron circuit comprises an electron discharge device provided with an anode, a cathode and two control electrodes, means for maintaining said anode at a positive potential with respect to the cathode, means for maintaining one of the control electrodes at a higher positive potential than said anode with respect to the cathode and means for applying a potential to the contro-l electrode and a glow discharge tube circuit including a condenser and a charging means therefor connected between the cathode of said electron -discharge device and one of the quencies by means of a continuously variable u tuning element, means for operating said detector tube above and below the point of oscillation thereof to produce super-regenerative effects comprising, an electron discharge device provided with anode, cathode, control electrode and an y auxiliary electrode, energizing means for said electrodes whereby the auxiliary electrode is maintained at a higher positive potential with respect to the cathode than the positive potential of the anode, a variable resistance circuit shunted j across said electron discharge device from the anode to the cathode thereof and means including a glow discharge tube, a condenser and a charging circuit therefor for periodically varying the value of said variable condenser whereby i;

the characteristics of the electron discharge tube are periodically varied'.

8. A system as described in the next preceding claim wherein said variable resistance comprises a space discharge device having an anode, a I

cathode and a control grid and wherein said glow discharge tube, condenser and charging circuit arrangement affects both said tube and the rst named electron discharge device.

9. In a receiver of the super-regenerative type .y

a detector tube, a high frequency resonant circuit associated therewith, a negative resistance device comprising a tub-e of the screen grid type associated with the resonant circuit, a periodic circuit associated with the negative resistance device, said periodic circuit operating at a frequency lower than the frequency of the resonant circuit and means for applying operating potentials to the elements of the screen grid tube so that said tube operates around the bend at one of the ends of the negative resistance portion of its plate current-plate voltage characteristic curve whereby oscillations are alternately and periodically set up and quenched in the resonant circuit associated with the detector tube, the period of setting up and quenching being determined by the frequency of operation of the periodic circuit.

10. In a super-regenerative receiver,-a detector circuit including a thermionic tube provided with an input circuit and an output circuit, the input circuit including signal input means adapted to be tuned over a range of frequencies, a second tube, circuits for said second tube for operating the tube as a dynatron oscillator and Vfor electrically coupling the tube to said input circuit, said oscillator circuit being arranged so as to alternately and periodically impress upon the input circuit of the detector tube negative and positive resistance effects to thereby cause the detector tube to alternately and periodically operate above and below the point of oscillation to produce super-regenerative action.

NOEL MEYER RUST. ROBERT FRANCIS ONEILL. 

